The present invention relates to a gas turbine power plant and a method of operating same. More specifically, the present invention relates to a method and apparatus for regulating and augmenting the power output of a gas turbine power plant by varying the flow rate of steam injected into the gas turbine combustor.
A gas turbine is comprised of a compressor section that produces compressed air that is subsequently heated by burning fuel in a combustion section. The hot gas from the combustion section is directed to a turbine section where the hot gas is used to drive a rotor shaft, thereby producing shaft power. The shaft power is used to drive the compressor. The excess power not consumed by the compressor drives a generator that produces electrical power. The amount of power imparted to the shaft is a function of the mass flow and temperature of the hot gas flowing through the turbine.
Owing to their rapid response, gas turbines are often used in environments in which the power demand varies. Traditionally, variations in power output have been accomplished by varying the rate at which fuel was burned in the combustor and, therefore, the temperature of the hot gas expanded in the turbine. However, such a method of regulating power output suffers from several drawbacks. First, the maximum temperature to which the hot gas may be heated is limited due to limitations on the strength of the components in the turbine at high temperature. Second, variations in gas temperature can induce transient thermal stresses in the turbine components due to differential thermal expansion. Therefore, frequent variations in hot gas temperature can have a deleterious effect on the thermal fatigue life of the turbine components.
The combustion process in a gas turbine typically results in the generation of oxides of nitrogen (NOx), which is considered an atmospheric pollutant. In the past steam or water has been injected into the combustor for the purpose of reducing the flame temperature and, hence, the rate of NOx formation. While it is known that injecting steam into the combustor increases the power output of the turbine, in the past, the amount of steam that could be safely injected without causing excessive back pressure in the compressor was limited by the flow capacity of the turbine, which was typically designed for dry operation. Hence, the ability to utilize steam injection for power augmentation was limited.
Therefore, it is desirable to provide a gas turbine into which large amounts of steam can be safely introduced in order to augment the power output of the turbine, and in which the power output may be regulated by varying the amount of steam introduced.